Sz stranded tight-buffered ribbon stacks with binder film

ABSTRACT

An optical fiber cable including a central strength member, a first plurality of tight-buffered ribbon stacks, a binder film, and a cable sheath. The central strength member extends along a longitudinal axis of the optical fiber cable. The tight-buffered ribbon stacks are SZ-stranded around the central strength member. An interstitial space is provided between adjacent tight-buffered ribbon stacks. A binder film continuously and contiguously surrounds the first plurality of tight-buffered ribbon stacks along the longitudinal axis. The binder film includes first portions and at least one second portion. Each of the at least one second portion of the binder film extends into one of the interstitial spaces of the first plurality of tight-buffered ribbon stacks. The cable sheath continuously and contiguously surrounds the binder film along the longitudinal axis, and the cable sheath is coupled to the first portions of the binder film.

CROSS-REFERENCED TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Application Ser. No. 62/869,920 filed on Jul. 2, 2019,the content of which is relied upon and incorporated herein by referencein its entirety.

BACKGROUND

The disclosure relates generally to an optical fiber ribbon cable andmore particularly to an optical fiber cable having a high fiber densitycontained within small diameter through the use of tight-buffered ribbonstacks SZ-stranded around a central strength member and held in place bya binder film. Optical fiber cables carry data in the form of light overlong distances. A variety of different optical fiber cables are used totransmit data across a network. Distribution cables carry data from adata center to various nodes where branches are split off to variousnetwork subnodes. Eventually, the optical fiber cable is subdivided toindividual premises. The number of optical fibers in each leg varies asdoes the size of the cable and the methods of installation. Thus, cablesof a variety of different types, sizes, and fiber counts are needed toefficiently service the entire network.

SUMMARY

In one aspect, the present disclosure relates to an optical fiber cableincluding a central strength member, a first plurality of tight-bufferedribbon stacks, a binder film, and a cable sheath. The central strengthmember extends along a longitudinal axis of the optical fiber cable. Thetight-buffered ribbon stacks are SZ-stranded around the central strengthmember. An interstitial space is provided between adjacenttight-buffered ribbon stacks. A binder film continuously andcontiguously surrounds the first plurality of tight-buffered ribbonstacks along the longitudinal axis. The binder film includes firstportions and at least one second portion. Each of the at least onesecond portion of the binder film extends into one of the interstitialspaces of the first plurality of tight-buffered ribbon stacks. The cablesheath continuously and contiguously surrounds the binder film along thelongitudinal axis, and the cable sheath is coupled to the first portionsof the binder film

In another aspect, the present disclosure relates to a method ofpreparing an optical fiber cable. In the method, a plurality oftight-buffered ribbon stacks are SZ-stranded around a central strengthmember extending along a longitudinal axis of the optical fiber cable. Abinder film is extruded around the plurality of tight-buffered ribbonstacks. The binder film drawn into at least one interstitial spacebetween adjacent tight-buffered ribbon stacks of the plurality oftight-buffered ribbon stacks. Further, the binder film is contacted withmolten cable sheath material to form a cable sheath.

In still another aspect, the present disclosure relate an optical fibercable. The optical fiber cable includes a central strength memberextending along a longitudinal axis of the optical fiber cable. Theoptical fiber cable also includes a first plurality of tight-bufferedribbon stacks that are SZ-stranded around the central strength member.An interstitial space is provided between adjacent tight-buffered ribbonstacks. Each of the first plurality of tight-buffered ribbon stackscomprises a second plurality of optical fiber ribbons surrounded by abuffer tube, and each of the first plurality of tight-buffered ribbonstacks has a rectangular cross-section. A binder film that continuouslyand contiguously surrounds the first plurality of tight-buffered ribbonstacks along the longitudinal axis. The binder film includes at leastone bent portion, and each of the at least one bent portion of thebinder film extends into one of the interstitial spaces of the firstplurality of tight-buffered ribbon stacks. Further, the optical fibercable includes a cable sheath that continuously and contiguouslysurrounds the binder film along the longitudinal axis. The cable sheathhas an outer surface defining an outermost surface of the optical fibercable. In the optical fiber cable, the first plurality of tight-bufferedribbon stacks includes at least 864 optical fibers and wherein the outersurface defines an outer diameter of no more than 21.5 mm.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawing.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is included to provide a further understandingand are incorporated in and constitute a part of this specification. Thedrawing illustrates one or more embodiment(s), and together with thedescription serves to explain principles and the operation of thevarious embodiments.

FIG. 1 depicts an optical fiber cable having SZ-stranded tight-bufferedrigidly stranded ribbon stacks bound with a binder film, according to anexemplary embodiment.

FIGS. 2A-2C depict various orientations of the tight-buffered ribbonstacks with respect to various polar positions during SZ-stranding,according to an exemplary embodiment.

FIG. 3 depicts the reversing of SZ-stranding of the tight-bufferedribbon stacks, according to an exemplary embodiment.

FIG. 4 depicts another embodiment of an optical fiber cable having anelastic binder film around the SZ-stranded tight-buffered ribbon stacks,according to an exemplary embodiment.

FIG. 5 is a flow diagram of a method of preparing the optical fibercable of FIG. 1, according to an exemplary embodiment.

DETAILED DESCRIPTION

Various embodiments of an optical fiber cable containing a plurality oftight-buffered ribbon stacks SZ-stranded around a central strengthmember and secured with a binder film are provided. The cable asdescribed is able to provide a high fiber density (e.g., at least 864optical fibers) while also maintaining a small diameter (e.g., such thatthe optical fiber cable can be pulled through a 1″ duct). As will bediscussed in detail below, the binder film, in embodiments, is expandedto provide free space for the optical fiber ribbons to shift into theirlowest energy positions. In another embodiment, the binder film iselastic so that the tight-buffered ribbon stacks are able to shifteasily when external forces impinge upon the cable. Also disclosedherein are various methods to manufacture an optical fiber cable havinga binder film extruded over SZ-stranded tight-buffered ribbon stacks.These and other aspects and advantages will be discussed in relation tothe embodiments provided herein. The embodiments of the optical fibercable disclosed herein are provided by way of example and not by way oflimitation.

FIG. 1 depicts an embodiment of an optical fiber cable 10 according tothe present disclosure. The optical fiber cable 10 includes a centralstrength member 12 extending along a longitudinal axis of the opticalfiber cable 10. In the embodiment depicted, the central strength member12 has a central rod element 14 and a coating layer 16. In embodiments,the central rod element 14 is a glass-reinforced plastic rod, but inother embodiments, the central rod element 14 may be, e.g., a metalwire. In embodiments, the coating layer 16 is a foamed material, such asfoamed linear low density polyethylene (LLDPE). The optical fiber cable10 has a plurality of tight-buffered ribbon stacks 18 stranded aroundthe central strength member 12. The tight-buffered ribbon stacks 18include a plurality of optical fiber ribbons 20. Each optical fiberribbon 20 has a plurality of optical fibers 22 arranged in a planar row.As can be seen in FIG. 1, the optical fiber ribbons 20 are surrounded bya buffer tube 24 that is in contact with the top, bottom, and sides ofthe stack of optical fiber ribbons 20. The tight-buffered ribbon stacks18 are in contrast to other cable designs that utilize a loose-tubeconfiguration in which the stacks of optical fiber ribbons aresurrounded by a substantial amount of free space within the buffer tube(e.g., 60% of the cross-sectional area being free space). Thus, as usedherein, a “tight-buffered ribbon stack” refers to a stack of opticalfiber ribbons surrounded by a buffer tube with there being 10% or lessof free space surrounding the stack of optical fibers in across-sectional area within the buffer tube. As depicted in FIG. 1, onlyone of the tight-buffered ribbon stacks 18 shows the optical fiberribbons 20 and optical fibers 22. The other tight-buffered ribbon stacks18 are depicted schematically, showing only their rectangularcross-section associated with the tight buffer tube 24 and stack ofribbons 20 (FIG. 4 depicts the tight-buffered ribbon stacks 18 in moredetail).

In embodiments, the optical fiber cable 10 includes from three to twelvetight-buffered ribbon stacks 18. In embodiments, each tight-bufferedribbon stack 18 includes from four to sixteen optical fiber ribbons 20,and in embodiments, each optical fiber ribbon 20 includes from four totwenty-four optical fibers 22. In the embodiment depicted, the opticalfiber cable 10 includes six tight-buffered ribbon stacks 18 with eachhaving twelve optical fiber ribbons 18, and each optical fiber ribbon 18has twelve optical fibers 22. Thus, the optical fiber cable 10 includes12×12×6 optical fibers 22 (or 864 optical fibers 22). In embodiments,the individual optical fibers 22, the optical fiber ribbons 20, and thetight-buffered ribbon stacks 18 are color-coded according totelecommunication standards for identification purposes.

In the embodiment depicted, the tight-buffered ribbon stacks 18 have arectangular cross-section. In embodiments, the tight-buffered ribbonsstacks 18 have a width W of from 1 mm to 10 mm and a height H of from 1mm to 10 mm. In the embodiment depicted (having twelve optical fiberribbons 20 with twelve optical fibers 22 each), the width is 3.6 mm andthe height is 4.2 mm.

The rigidly stranded tight-buffered ribbon stacks 18 are SZ-strandedaround the central strength member 12. That is, the tight-bufferedribbon stacks 18 are pre-stranded prior to SZ stranding them. Inembodiments, the SZ-stranding reverses every 275.5° during strandingwith a distance between reversals (S to Z or Z to S) of around 400 mm.The reversal at 275.5° is selected in embodiments because this degree ofwinding balances tension and compression strains on the surfaces of thetight-buffered ribbon stacks 18. Further, in embodiments, theSZ-stranding has a laylength of from 300 mm to 1200 mm. Althoughdescribed with an optimal reversal at 275.5°, reversals in cables may besituated through a range of 270°-280°.

FIGS. 2A-2C depict the progression of the tight-buffered ribbon stacks18 during SZ-stranding. As shown in FIG. 2A, the optical fiber ribbonstacks 18 are each stranded around the central strength member 12 andtwisted about themselves (by virtue of the pre-stranding). Thus, in FIG.2A, the tight-buffered ribbon stacks 18 are at a 0° position with theirshort side against the central strength member 12. As the tight-bufferedribbon stacks 18 continue to be stranded around the central strengthmember 12, the corner of each tight-buffered ribbon stack 18 comes intocontact with the central strength member 12 in a 137.5° position asshown in FIG. 2B. As mentioned above, the central strength member 12 maybe overcoated with foam to substantially distribute the load on thediagonals of the tight-buffered ribbon stacks 18 in contact with thecentral member. Upon rotating 275.5° as shown in FIG. 2C, the long sideof each tight-buffered ribbon stack 18 is in contact with the centralstrength member 12. Upon reaching the 275.5° position, thetight-buffered ribbon stacks 18 are stranded back the other direction tothe 0° position. It should be noted that the depictions in FIGS. 2A-2Cof the tight-buffered ribbon stacks 18 and their relative orientation ata given angular position are for illustrative purposes. The actualorientation of the tight-buffered ribbon stacks 18 for a given angularposition may be different depending, e.g., on the degree of SZ-strandingand the laylength. FIG. 3 depicts a perspective view of a section ofcable with the tight-buffered ribbon stacks 18 SZ-stranded around thecentral strength member 12. As can be seen, the stranding changes from Sto Z at a reversal point. FIG. 3 also depicts the twisting(pre-stranding) of the individual tight-buffered ribbon stacks 18.

Returning to FIG. 1, the tight-buffered ribbon stacks 18 are held intheir positions around the central strength member 12 by a binder film26. In embodiments, the binder film 26 is extruded around thetight-buffered ribbon stacks 18 simultaneously with or immediately afterthe stranding of the tight-buffered ribbon stacks 18 around the centralstrength member 12. In embodiments, the binder film 26 is extrudedaround the tight-buffered ribbon stacks 18 while a vacuum is applied onthe interior of the binder film 26. In embodiments, this causes thebinder film 26 to be drawn into one or more of the interstitial spaces28 between adjacent tight-buffered ribbon stacks 18, forming at leastone bent region 30 in the binder film 26. When the binder film 26 cools,any bent regions 30 formed remain in their respective interstitialspaces 28, which helps to maintain the SZ-stranding of thetight-buffered ribbon tubes 18 around the central strength member 12.

In embodiments, the binder film 26 is formed from an elastic material,such as impact-modified polypropylene copolymer, among others. In otherembodiments, the binder film 26 is formed from at least one of linearlow-density polyethylene (LLDPE), a polyester, a polyamide, or apolypropylene copolymer. In embodiments, the binder film 26 has athickness T₁ of from 0.02 mm to 0.15 mm.

Disposed around the binder film 26 is a cable sheath 32. The cablesheath 32 has an interior surface 34 and an exterior surface 36. Inembodiments, the exterior surface 36 defines the outermost surface ofthe optical fiber cable 10. In embodiments, the interior surface 34 isat least partially in contact with the binder film 26. For example, inembodiments, the interior surface 34 is in contact with portions 38 ofthe binder film 26 between bent regions 30. In embodiments, the cablesheath 32 is extruded around the binder film 26 in such a manner thatmolten cable sheath material contacts the portions 38 of the binder film26, causing the portions 38 to decrease in modulus. In embodiments, atthe same time as the molten cable sheath material contacts the portions38 of the binder film 26, the interior of the binder film 26 may bepressurized to cause the binder film 26 to expand and create free spacewithin the binder film 26 for the tight-buffered ribbon stacks 18. Inembodiments, the portions 38 that contact the molten cable sheathmaterial expand to a greater degree than the bend regions 30. Extrudingthe cable sheath 32 around the binder film 26 couples the cable sheath32 to the binder film 26. In embodiments, the binder film 26 (andinterior components) are interference fit within the cable sheath 32.

In certain embodiments in which an elastic material is used for thebinder film 26, the binder film 26 is not expanded while the cablesheath 32 is formed. FIG. 4 depicts an embodiment of the elastic binderfilm 26 embodiment. As can be seen in FIG. 4, the outermost extent ofthe elastic binder film 26 essentially defines the inner diameter of thecable sheath 32. Additionally, a layer of water-blocking tape 42 iswrapped around the binder film 26 such that the water-blocking tape 42is in contact with the interior surface 34 of the cable sheath 32. Ascan be seen in a comparison with FIG. 1, the elastic binder film 26keeps the tight-buffered ribbon stacks 18 tightly against the centralstrength member 12. As can be seen in FIG. 1, by comparison, theexpanded binder film 26 does not hold the tight-buffered ribbon stacks18 tightly against the central strength member 12 (including embeddingthe tight-buffered ribbon stacks 18 into the foamed coating layer 16).In embodiments of either the expanded or elastic binder film 26, thebinder film 26 provides at least 40% of free space for the movement ofthe tight-buffered ribbon stacks 18. In other embodiments, the binderfilm 26 provides up to 60% of free space for movement of thetight-buffered ribbon stacks 18. The cable construction disclosed hereinpermits the use of continuously reversing straining lay at 275.5° whichreduces the requisite free space by placing the units in a reverse bendwithout additional torsion.

In embodiments, the cable sheath 32 is formed from, e.g., medium densitypolyethylene (HDPE), or another jacketing material. In embodiments, thecable sheath 32 may include one or more strength elements 40. Forexample, in the embodiment shown in FIG. 4, the cable 10 includes fourstrength elements 40. In the embodiment of FIG. 4, the strength elements40 are arranged in diametrically opposed pairs, which creates apreferred bend axis. In embodiments, the strength elements are, e.g.,glass reinforced plastic rods or steel wires. In embodiments, thestrength elements 40 have a diameter of from 1 mm to 2 mm, moreparticularly about 1.6 mm. In embodiments, the cable sheath 32 has athickness T₂ between the inner surface 34 and the outer surface 36 thatis, on average, from 2 mm to 3 mm.

In a particular, commercially envisioned embodiment, the optical fibercable 10 has six tight-buffered ribbon stacks 18, each having twelveoptical fiber ribbons 20 with twelve optical fibers 22 each for 864total optical fibers 22. In embodiments, the optical fiber cable has anouter diameter OD of 21.5 mm or less. In other embodiments, the opticalfiber cable 10 has an outer diameter OD of 20.3 mm or less, and in stillother embodiments, the optical fiber cable 10 has an outer diameter ODof 20 mm or less. Further, in embodiments, the optical fiber cable 10 isable to be pulled through a 1-inch duct. The construction of the opticalfiber cable 10 provides sufficient free space so that the tight-bufferedribbon stacks 18 can move without causing attenuation or fiber damagewhen the optical fiber cable 10 is routed around bends in a duct.

Having described the structure of the optical fiber cable 10,embodiments of methods of preparing the optical fiber cable 10 will nowbe provided. FIG. 5 depicts a flow diagram of a method 100 formanufacturing the optical fiber cable 10 according to the presentdisclosure. In a first step 110, the tight-buffered ribbon stacks 18 areSZ-stranded around the central strength member 12. In a particularembodiment, an SZ stranding lay-plate is extended through an extrusioncrosshead. The lay-plate guides and oscillates the tight-buffered ribbonstacks 18 to introduce a helix as the tight-buffered ribbon stacks 18are formed around the central strength member 12. In an embodiment, thetight-buffered ribbon stacks 18 are planetarily SZ stranded. Further, inembodiments, the tight-buffered ribbon stacks 18 are rigidlyprestranded, and in view of their rectangular in cross section, thesurface that presents itself to the central member during the planetaryaction of stranding changes as the each tight-buffered ribbon stack 18forms a helix. The diagonal of each rectangular tight-buffered ribbonstack 18 is the largest dimension. The diameter of the central strengthmember 12 plus the unit diagonal length sum to comprise the strandingmean diameter or pitch circle of the tight-buffered ribbon stacks 18.When the tight-buffered ribbon stacks 18 are stranded around amoderately rigid or rigid central strength member 12, only the face thatforms on the diagonal of the unit is tangent to the central strengthmember 12. The balance of each tight-buffered ribbon stack 18 does notcontact the central strength member 12 as it is bent. The induced twistform the secondary stranding operation is removed by the planetarystranding action.

In a second step 120, the binder film 26 is extruded around thetight-buffered ribbon stacks 18. While the first step 110 and secondstep 120 are depicted as separate steps, the first step 110 and thesecond step 120 may be performed simultaneously, or the second step maybe performed immediately after the first step 110. The first step 110and the second step 120 are performed close together, at least in part,because the binder film 26 retains the tight-buffered ribbon stacks 18in their SZ-stranded configuration. Additionally, a vacuum is applied onthe interior of the binder film 26 to draw the binder film 26 into theinterstitial spaces 28 between the tight-buffered ribbon stacks 18.While the binder film 26 cools, in embodiments, the lay of thetight-buffered ribbon stacks 18 is retained by a coupling caterpullerwith opposing grooved belts.

After the binder film 26 cools, according to one embodiment of themethod 100 for forming an expanded binder film 26, the binder film 26 ispressurized prior to sheathing in a third step 130. In such anembodiment, the binder film 26, tight-buffered ribbon stacks 18, andcentral strength member 12 are connected to a rotating union on apayoff. A pressurized air supply is provided to sustain pressure duringthe run. In embodiments, the interior of the binder film 26 is pressuredto, e.g., 0.5 bar (7.5 psig) with compressed air. At this pressure atroom temperature, an increase in the diameter of the strandedtight-buffered ribbon stacks 18 is detectable but remains relativelytight against the central strength member 12. The interior of the filmcould be coated with a reactive substance such as powdered sodiumbicarbonate which would release CO₂ gas when heated due to contact withthe molten jacket polymer. A reactive element could alternatively beheated via electromagnetic induction. The central strength member 12 orother embedded element, including the buffer tubes 24 of thetight-buffered ribbon stacks 18, could function to expand the binderfilm 26 temporarily during application of the binder film 26 to push thestranded tight-buffered ribbon stacks 18 outward against the binder film26 to produce the expanded binder film 26. In embodiments in which thebinder film 26 is elastic, this third step 130 may be skipped.

In a fourth step 140, the binder film 26 is contacted with molten cablesheath material, which lowers the modulus of portions 38 the binder film26. If the third step 130 is performed, the portions of the binder film26 with lower modulus expand outward while the bent portions 30 of thebinder film 26 within the interstitial spaces 28 remain cooler and onlymove outward while largely retaining their shape, their axial location,and their polar position in the cross section. In embodiments, thisprovides about free space of at least about 40% in the cross-sectionalarea of the expanded binder film 26. In an embodiment, a pair ofopposing grooved belts engage the cable sheath 32, controlling theoutward diameter excursion resulting from the induced internal pressureuntil the sheath modulus has increased to a level to elastically controlit. In another embodiment, the outward excursion of the molten cablesheath 32 is constrained by sequential split orifices of varyingdiameter or the same diameter submerged in a cooling bath of water.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred. In addition, as used herein, thearticle “a” is intended to include one or more than one component orelement, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modifications,combinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An optical fiber cable, comprising: a centralstrength member extending along a longitudinal axis of the optical fibercable; a first plurality of tight-buffered ribbon stacks that areSZ-stranded around the central strength member, wherein an interstitialspace is provided between adjacent tight-buffered ribbon stacks; abinder film that continuously and contiguously surrounds the firstplurality of tight-buffered ribbon stacks along the longitudinal axis,the binder film comprising first portions and at least one secondportion, wherein the at least one second portion of the binder filmextends into the interstitial space between the adjacent tight-bufferedribbon stacks; and a cable sheath that continuously and contiguouslysurrounds the binder film along the longitudinal axis, wherein the cablesheath is coupled to the first portions of the binder film.
 2. Theoptical fiber cable of claim 1, wherein the binder film comprises anelastic material.
 3. The optical fiber cable of claim 2, wherein theelastic material comprises impact-modified polypropylene copolymer. 4.The optical fiber cable of claim 1, wherein the optical fiber cablecomprises at least 40% free space in a cross-sectional area on aninterior of the cable sheath.
 5. The optical fiber cable of claim 1,wherein the binder film comprises at least one of linear low-densitypolyethylene, a polyester, a polyamide, or a copolymer of polypropylene.6. The optical fiber cable of claim 1, wherein the first plurality oftight-buffered ribbon stacks comprises at least 864 optical fibers, andwherein the cable sheath comprises an outer surface, and wherein theouter surface defines an outer diameter of no more than 21.5millimeters.
 7. The optical fiber cable of claim 1, wherein the centralstrength member comprises a central rod element and a coating layer andwherein the coating layer comprises a foam material.
 8. The opticalfiber cable of claim 1, wherein the first plurality of tight-bufferedribbon stacks has a rectangular cross-section.
 9. The optical fibercable of claim 1, wherein each of the first plurality of tight-bufferedribbon stacks comprises a second plurality of optical fiber ribbonssurrounded by a buffer tube and wherein 10% or less of a cross-sectionalarea of each of the first plurality of tight-buffered ribbon stacks isfree space within the buffer tube.
 10. The optical fiber cable of claim1, wherein the first plurality of tight-buffered ribbon stacks isSZ-stranded with a reversing lay between 270° and 280°.
 11. A method ofpreparing an optical fiber cable, comprising the steps of: SZ-strandinga plurality of tight-buffered ribbon stacks around a central strengthmember extending along a longitudinal axis of the optical fiber cable;extruding a binder film around the plurality of tight-buffered ribbonstacks; drawing the binder film into at least one interstitial spacebetween adjacent tight-buffered ribbon stacks of the plurality oftight-buffered ribbon stacks; contacting the binder film with moltencable sheath material to form a cable sheath about the binder film. 12.The method of claim 11, further comprising the step of expanding thebinder film while contacting the binder film with the molten cablesheath material.
 13. The method of claim 12, wherein the step ofexpanding the binder film further comprises filling the binder film witha pressurized fluid.
 14. The method of claim 12, further comprising thestep of coating an interior of the binder film with a reactive material,wherein when the binder film is contacted with the molten cable sheathmaterial, the reactive material produces gas for expanding the binderfilm.
 15. The method of claim 11, further comprising the step of pullingthe binder film, the plurality of tight-buffered ribbon stacks, and thecentral strength member through a water bath using a caterpuller. 16.The method of claim 11, wherein the step of SZ-stranding furthercomprises reversing a lay at 275.5°.
 17. The method of claim 11, whereinthe central strength member comprises a central rod element and acoating layer, the coating layer comprising a foam material.
 18. Anoptical fiber cable, comprising: a central strength member extendingalong a longitudinal axis of the optical fiber cable; a first pluralityof tight-buffered ribbon stacks that are SZ-stranded around the centralstrength member, wherein an interstitial space is provided betweenadjacent tight-buffered ribbon stacks, wherein each of the firstplurality of tight-buffered ribbon stacks comprises a second pluralityof optical fiber ribbons surrounded by a buffer tube, and wherein eachof the first plurality of tight-buffered ribbon stacks has a rectangularcross-section; a binder film that continuously and contiguouslysurrounds the first plurality of tight-buffered ribbon stacks along thelongitudinal axis, the binder film comprising bent portions, wherein thebent portions of the binder film extend into each interstitial space ofthe first plurality of tight-buffered ribbon stacks; and a cable sheaththat continuously and contiguously surrounds the binder film along thelongitudinal axis, wherein the cable sheath comprises an outer surfacedefining an outermost surface of the optical fiber cable; wherein thefirst plurality of tight-buffered ribbon stacks comprises at least 864optical fibers and wherein the outer surface defines an outer diameterof no more than 21.5 millimeters.
 19. The optical fiber cable of claim18, wherein the binder film comprises an elastic material.
 20. Theoptical fiber cable of claim 18, wherein the optical fiber cablecomprises at least 40% free space in a cross-sectional area on aninterior of the cable sheath.